Consumer Unit 8m from cutout

[monkey5]

apologies if this is a daft question but its the first time ive actuall come across this. went to look at upgrading old fuse box to new Con unit and found that fuse box location is about 8m from cutout so at the minute 16mm2 meter tails go to switched fuse unit with 45a fuse carrier then this feeds fuse box with 16mm2 twin and earth.

is this the normal way of doing this if tails over the recommended 3m?

was going to upgrade swiched fuse with 80a (80a in cutout too)with 25mm2 tails from cutout to switched fuse then should i use 25mm2 tails from switch fuse to new con unit or would 16mm2 suffice (its a bungalow so would be in loft space)

was going to move switched fuse into loft so not on bedroom wall, would this be ok?

its tncs

cheers wayne

 

[tom1]

i would say the switch fuse in the loft would be an accessibility issue if it did ever trip, will a 60 amp switch fuse do then keep it in 16mm twin.

thats my take but see what other say

 

[ianmacd]

I would also suggest 60A to allow discrimination with the service fuse.

 

[monkey5]

point taken with fuse, will go with 60a

cheers

 

[PIP IOM]

check the 60amp switch fuse can take 25mm tails before you buy it. I got one from CEF and they wouldn't fit 16mm max.

 

[monkey5]

check the 60amp switch fuse can take 25mm tails before you buy it. I got one from CEF and they wouldn't fit 16mm max.

will do cheers for heads up

 

[steptoe]

Im not sure on this, but I didnt think you could run tails that distance,

maybe its just me, but I would deffo consider it bad practice,

wouldnt you be better with some concentric or similar?

 

[Riggy]

Im not sure on this, but I didnt think you could run tails that distance,maybe its just me, but I would deffo consider it bad practice,

wouldnt you be better with some concentric or similar?

No problem for me as long as there are no issues requiring greater mechanical protection.

 

[steptoe]

No problem for me as long as there are no issues requiring greater mechanical protection.

must just be something Ive got in my head from somewhere, :Blushing

 

[binky]

Im not sure on this, but I didnt think you could run tails that distance,maybe its just me, but I would deffo consider it bad practice,

wouldnt you be better with some concentric or similar?

DNOs always had their own ideas about tail length being protected by their equipment, hence all the numbers like 3m that people discuss, and use of switch-fuses so installation has its own fuse protection. However, on a new build in Salcombe I came across 30m tails and contacted local DNO - in short DNO lost court case for arbitary restriction on tail length. The courts considered the argument that cut-out fuse protects tails, a legitimate compliance with BS7671, without the use of switch-fuses etc. etc.

In short as long as the circuit complies with regs, you no longer need the switch-fuse. Does mean seal fairies will be needed to change fuses though

 

[TonyCE]

However, on a new build in Salcombe I came across 30m tails and contacted local DNO - in short DNO lost court case for arbitary restriction on tail length. The courts considered the argument that cut-out fuse protects tails, a legitimate compliance with BS7671, without the use of switch-fuses etc. etc.

Do you have any details on the court case?

I'd like to quote this at the NICEIC at some point. The only information I've seen on this previously is that in the OSG it says that the distributor sets the max length of the tails and the distributor I have discussed this with also quoted 3m max.

 

[Andy™]

Im not sure on this, but I didnt think you could run tails that distance,maybe its just me, but I would deffo consider it bad practice,

wouldnt you be better with some concentric or similar?

dont take this the wrong way, but it seems as though if its not how you would do it, then 'its bad practice'

there are many ways to achieve the same thing. and meter tails are no different to a final circuit.

also, the tails may required an RCD (usual T&E conditions)

 

[ianmacd]

Do you have any details on the court case? I'd like to quote this at the NICEIC at some point. The only information I've seen on this previously is that in the OSG it says that the distributor sets the max length of the tails and the distributor I have discussed this with also quoted 3m max.

Diud you tell DNO you will be fusing it down? before your long tail run and that tails will be installed in accordance with 7671?

 

[binky]

Do you have any details on the court case? .

Unfortunately not, and local DNO doesn't publicise case 'cos they don't like it. Prefer old method personally.

 

[initforthemoney]

They can run their submains as long as they like.

Its us that should provide the fault protection via switch fuse.

Whatever they say, i would still install one.

 

[steptoe]

[quote name='Andy

 

[Andy™]

edit, usual T&E conditions do NOT apply to single conductors

they do with regard to RCD requirements for being buried in a wall etc

 

[green-hornet]

[quote name='Andy

 

[Andy™]

I can not see how damage to a concealed Live cable would be picked up by any RCD, unless the damage was such that an imbalance was shown via the neutral.If it was twin and earth then any insulation damage could be detected before any serious damage or harm could occur.

you can easily hit a T&E, only hit live, and not trip an RCD. exactly the same as if you hit a DI live. only time it will trip is if you hit both L&E, or you get a shock

 

[green-hornet]

I agree and its perfectly feasable, however the chances are slimmer with T&E than a seperate Live. This is one of the reasons why those orrible single live and earth cables where designed.

If I had to move any cu this distance from supply I would go with conc or armour as first choice, and doing so would not need to RCD, just provide isolation.